Multiple choice

A boat goes 36 km upstream in 4.5 hours and 72 km downstream in 6 hours. Find the speed of the current.

  1. 2 km/hr

  2. 3 km/hr

  3. 10 km/hr

  4. 12 km/hr

  5. None of these

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let boat speed = b, current speed = c. Upstream speed = b - c = 36/4.5 = 8 km/hr. Downstream speed = b + c = 72/6 = 12 km/hr. Subtracting the two equations: (b + c) - (b - c) = 12 - 8 = 4 = 2c, so c = 2 km/hr. The speed of the current is 2 km/hr.